Inlet system for an MOCVD reactor

ABSTRACT

The invention relates to a device for depositing especially crystalline layers on at least one especially crystalline substrate in a process chamber comprising a top and a vertically opposing heated bottom for receiving the substrates. A gas-admittance body forming vertically superimposed gas-admittance regions is used to separately introduce at least one first and one second gaseous starting material, said starting materials flowing through the process chamber with a carrier gas in the horizontal direction. The gas flow homogenises in an admittance region directly adjacent to the gas-admittance body, and the starting materials are at least partially decomposed, forming decomposition products which are deposited on the substrates in a growth region adjacent to the admittance region, under continuous depletion of the gas flow. An additional gas-admittance region of the gas-admittance body is essential for one of the two starting materials, in order to reduce the horizontal extension of the admittance region.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of pending Internationalpatent application PCT/EP2005/050765 filed on Feb. 23, 2005 whichdesignates the United States and claims priority from German patentapplication 10 2004 009 130.7 filed on Feb. 25, 2004, the content ofwhich is incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to a device for depositing in particularcrystalline layers on one or more in particular crystalline substratesin a process chamber, which has a ceiling and a heated floor, verticallyopposite the ceiling, for receiving the substrates, with a gas inletmember, which forms gas inlet zones disposed vertically one above theother for introducing at least a first and a second gaseous startingmaterial separately from one another, which starting materials flow in ahorizontal direction together with a carrier gas through the processchamber, the stream of gas being homogenized and the starting materialsat least partially pre-decomposed in an inlet zone directly adjacent thegas inlet member, the decomposition products of which starting materialsare deposited on the substrates in a growing zone adjacent the inletzone, while the stream of gas is steadily depleted.

The invention additionally relates to a method for depositing inparticular crystalline layers on one or more in particular crystallinesubstrates in a process chamber, which has a ceiling and a heated floor,vertically opposite the ceiling, on which the substrates lie, in whichmethod at least a first and a second gaseous starting material areintroduced into the process chamber through gas inlet zones of a gasinlet member disposed vertically one above the other, which startingmaterials flow in a horizontal direction together with a carrier gasthrough the process chamber, the stream of gas being homogenized and thestarting materials at least partially pre-decomposed in an inlet zonedirectly adjacent the gas inlet member, the decomposition products ofwhich starting materials are deposited on the substrates in a growingzone adjacent the inlet zone, while the stream of gas is steadilydepleted.

BACKGROUND OF THE INVENTION

A device of this type and a method of this type are known from DE 100 43601 A1. This document describes a circular-symmetrical device fordepositing in particular III-V semiconductor layers on III-Vsemiconductor substrates. The known device has a circular-cylindricalprocess chamber extending in the horizontal plane. The floor of theprocess chamber is formed by a heated substrate holder. On the substrateholder there are a multiplicity of substrate carriers in circulararrangement around the center of the holder. One or more substrates maybe disposed on each of the substrate carriers. The substrate carriersare rotationally driven. The ceiling of the process chamber, oppositethe floor of the process chamber, may likewise be heated. At the centerof the ceiling there is a gas inlet member. This protrudes into theprocess chamber. The portion of the gas inlet member that protrudes intothe process chamber is water-cooled. The gas inlet member forms two gasinlet zones, lying vertically one above the other. The inlet zone thatis disposed immediately above the floor is located between the floorplate and an end face of the gas inlet member, which has at its centeran opening from which a hydride emerges together with a carrier gas.This hydride may be arsine, phosphine or ammonia. Above this inlet zonethere is a further inlet zone, through which a gaseous startingmaterial, likewise mixed in a carrier gas, is introduced into theprocess chamber. This gaseous starting material may be TMGa, TMIn orsome other metalorganic compound.

Under typical process conditions, the stream of the first startingmaterial, which flows through the gas inlet zone neighboring the floorof the process chamber, is considerably greater than that which flowsthrough the second gas inlet zone. The starting material which flowsthrough the first gas inlet zone is also of a considerably higherconcentration than the starting material which flows through the secondgas inlet zone, so that not only is the velocity of the gas flowingthrough the first gas inlet zone considerably greater than the velocityof the gas flowing through the second gas inlet zone, but the densitiesof the gases also differ considerably.

In an inlet zone directly adjoining the gas inlet member, the startingmaterials are partially thermally decomposed. In this zone, ahomogenization of the flow or a homogenization of the gas phase alsotakes place. The two starting materials must mix with each other. In agrowing zone adjoining the inlet zone downstream are the substrates. Inthis zone, the gas phase concentration of the reactants, and inparticular of the III component, decreases as the distance from the gasinlet member increases. This gas phase depletion is accompanied by afall in the growth rate as the distance from the gas inlet memberincreases. To make the growth more uniform, compensation is provided bythe rotation of the substrate carriers. These circumstances aredescribed by DE 100 57 134 A1.

The position of the limit between inlet zone and growing zone isdetermined by the maximum of the growth rate. This maximum lies wherethe pre-decomposition or homogenization of the gas phase and of thestream is substantially completed and the growth-limiting group IIIstarting materials are diffused by the dense highly concentrated streamof gas from the lower inlet. The maximum is intended to lie shortlybefore the beginning of the growing zone in the direction of flow.

If it is wished to increase the capacity of the known device, allowingmore substrates to be coated simultaneously, the extent of the growingzone must be increased. At the same time, however, the supply ofstarting materials must also be increased. If the stream of gas of thestarting materials into the process chamber is increased, the limitbetween inlet zone and growing zone shifts away from the gas inletmember. However, increasing the gas inlet zone in this way is undesired,since undesired adducts can form in this zone. On the other hand,however, the maximum of the growth rate must not lie within the growingzone, in order to ensure homogeneous growth of the layers on thesubstrates. In addition, increasing the inlet zone entails either areduction of the growing zone or a structural increase in the size ofthe entire process chamber. The latter is undesired for reasons of cost.

It is consequently an object of the invention to specify measures as tohow the useful surface area in a process chamber can be increased. Thisincrease is at the same time to be possible without reducing the packingdensity of the substrates on the substrate holder.

SUMMARY OF THE INVENTION

The object is achieved by the invention specified in the claims.

Claim 1 provides first and foremost an additional gas inlet zone of thegas inlet member for one of the two starting materials, to reduce thehorizontal extent of the inlet zone. According to the proposal of claim2, to reduce the horizontal extent of the inlet zone, one of the twostarting materials is to be introduced into the process chamber not justthrough one gas inlet zone but through two gas inlet zones. The firststarting material, which is introduced through a gas inlet zoneneighboring the floor of the process chamber, is preferably alsointroduced through the additional gas inlet zone. This may beneighboring the ceiling of the process chamber. This has the consequencethat altogether three gas inlet zones are provided. The V component orthe hydride is introduced into the process chamber through the two outergas inlet zones neighboring the ceiling and the floor. The III componentis introduced into the process chamber through the middle gas inletzone, optionally provided with a pressure barrier. This component ispreferably a metalorganic compound, which is dissolved in a carrier gas,for example nitrogen or hydrogen. It is also possible in the case of thedevice according to the invention or the method according to theinvention for the first starting material to be introduced into theprocess chamber in a concentration that is 100 to 5000 times higher thanthe second starting material. The device according to the invention mayhave a heated floor. The ceiling may either be heated or not heated.Preferably, however, it is a hot-wall reactor with a heated floor and anon-heated ceiling. Furthermore, it is possible for the vertical size ofthe gas inlet zones neighboring the floor and the ceiling to be lessthan the vertical size of the middle gas inlet zone. The sum of the twosizes of the gas inlet zones neighboring the floor and the ceiling mayalso be less than the size of the middle gas inlet zone. The gas mayflow in through the outer gas inlet zones at a higher flow velocity thanthrough the middle gas inlet zone. The reactor may have a rotationallydriven substrate holder, as described by DE 100 43 601 A1. The substrateholder may in the same way have substrate carriers disposed around thecenter of the substrate holder in the manner of satellites. Altogether,there may be six substrate carriers, which surround the circular inletzone lying close together in a circular arrangement. The growing zonethen has an annular shape. Each individual substrate carrier may carry atotal of seven substrates. This achieves a high packing density. In away similar to in the prior art, the gas inlet member may bewater-cooled, so that abrupt heating of the process gas takes place whenit flows into the process chamber. The inlet member is designed in sucha way that each of the three or more inlet zones can be individuallysupplied with gas. Corresponding mass flow regulators and valves areprovided for this purpose. In particular, the middle gas inlet zone,which is associated with the metalorganic component, may have a pressurebarrier. This pressure barrier may consist of a porous material. Thisavoids back diffusion. The gas inlet member may, in a known manner, havea rotationally symmetrical shape, as described for example in DE 100 64941 A1. The substrate holder is heated. It is heated by means ofradiation and/or heat conduction. The heat for heating the floor may begenerated as infrared heat. Electrical resistance heating is alsopossible.

BRIEF DESCRIPTION OF THE DRAWINGS

An exemplary embodiment of the invention is explained below withreference to accompanying drawings, in which:

FIG. 1 shows the cross section through one half of a rotationallysymmetrical reactor in a broadly schematic representation,

FIG. 2 shows the radial variation in the growth rate, and

FIG. 3 shows the plan view of a substrate holder with altogether sixsubstrate carriers, which are in each case loaded with seven substrates.

DETAILED DESCRIPTION OF THE INVENTION

The exemplary embodiment shows a rotationally symmetrical reactor, inwhich the gases are introduced at the center and in which the gases arecarried away in the region of the periphery. However, the invention alsorelates to those reactors which have the form of a tube, in which thegas is introduced at one end and the gas is discharged at the other end.

A significant component is a gas inlet member 5. This is located wherethe gas is introduced into the process chamber, that is to say at thecenter in the case of a process chamber 1 of a circular-symmetricalshape. The gas inlet member 5 has three gas inlet zones 6, 7, 8,disposed vertically one above the other. The three gas inlet zones arelocated between the ceiling 2 and the floor 3 of the process chamber 1.

In the exemplary embodiment, the floor 3 is actively heated by suitablemeans. The ceiling 2 is indirectly heated by the heated floor 3 by meansof radiation and heat conduction. The heat for heating the floor 3 maybe generated as infrared heat. However, it is also envisaged to generatethe heat in the manner described by DE 100 43 601 A1, that is by highfrequency.

In the case of the exemplary embodiment, the process gas flows throughthe process chamber 1 from the center to the periphery. For depositingIII-V semiconductors, the V components are fed in as hydrides throughthe gas inlet zones 6, 8, which are directly neighboring the ceiling 2and the floor 3, respectively. In particular, PH₃, AsH₃ or NH₃ isintroduced through the gas inlet zones 6 and 8.

The metalorganic III component is introduced through the middle gasinlet zone 7, disposed between the outer gas inlet zones 6 and 8; inparticular, TMG or TMI or an Al compound is introduced here.

An annular pressure barrier of a porous, gas-permeable material isdesignated by the reference numeral 11. The III component flows throughthis together with the carrier gas. The gas which passes through theouter gas inlet zones 6 and 8 is of a greater density and mass flow thanthe gas which flows into the process chamber 1 through the middle gasinlet zone 7. The gas inflows in the gas inlet zones 6, 8 can be setindependently of the gas flow in the gas inlet zone 7.

Cross-pieces or separating elements by which the gases entering theprocess chamber through the gas inlet zones 6, 7, 8 are separated aredesignated by the reference numerals 12 and 13. Here, the representationis only schematic. It goes without saying that such gas conducting meansas pipes or ducts that are capable of conducting the gases flowingthrough the gas inlet zones 6, 7, 8 separately from one another from agas supply device to the reactor are provided.

In FIG. 2, the inlet zone is designated by EZ. Within this inlet zone,the reactive components entering the process chamber from the gas inletzones 6 and 8 or 7 are mixed. This substantially takes place bydiffusion. Adequate mixing is achieved by the limit of the inlet zonethat is represented in FIG. 2 as a dashed line. By this limit, the flowprofile in the process chamber has also been homogenized. Thepyrolytically decomposable components, and in particular the hydride,which is decomposable with more difficulty and flows into the processchamber 1 through the gas inlet zones 6 and 8, have likewise beenpartially pyrolytically decomposed by this limit. However, the radialwidth of the inlet zone EZ is so small that adduct formation between thecomponents is prevented to a sufficient extent.

The solid curve in FIG. 2 characterizes the growth rate in dependence onthe radial distance from the center of the process chamber 1. Themaximum 10 of the growth rate r lies shortly before the limit of theinlet zone EZ. In the region of the growing zone GZ adjoining the inletzone EZ in the radially outward direction, the growth rate r falls asthe radial distance R increases. This fall in the growth rate iscompensated by the rotation about their own axis of the circulardisk-shaped substrate carriers 9 represented in FIG. 3. The substratecarriers 9 may in this case be mounted on a gas cushion and—as describedin DE 100 43 601 A1—be rotationally driven by means of gas jets. Alsoserving to make the layer thickness more uniform over the substrates 4is the rotation of the entire substrate holder 3, which is formed by thefloor of the process chamber 1, about the axis of the process chamber.

As can be gathered from FIG. 3, the individual substrate carriers 9 havea diameter which is great enough to accommodate seven 2″ substrates inextremely closely packed formation. Altogether, six substrate carriersare disposed around the center of the substrate holder 3 in a uniformlydistributed manner.

The curve represented by a dashed-dotted line in FIG. 2 shows thevariation in the growth rate r with respect to the radial distance Rfrom the center of the process chamber 1 as it is in the prior art, inwhich a gas inlet member such as that described in DE 100 43 601 A1 isused. The additional gas inlet zone 8 for the V component has the effectthat the maximum of the growth rate r shifts toward a smaller radialdistance R.

It is provided that the vertical sizes of the gas inlet zones 6 and 8are each of the same size. The same amounts of gas per unit of time arealso preferably intended to flow through these gas inlet zones 6 and 8.The sizes of the gas inlet zones 6, 8 are less than the size of themiddle gas inlet zone 7. In particular, the sum of the sizes of the gasinlet zones 6 and 8 is less than the size of the middle inlet zone 7.

Model calculations in the case of a device of the prior art (DE 100 43601 A1) have shown that the different densities and the greatdifferences in the flow velocities of the gases entering the processchamber through the gas inlet zones produce an annular vortex underneaththe ceiling in the region of the inlet zone EZ. It has been observedthat a stream of gas with a gas which flows through an additional gasinlet zone 8 adjacent the ceiling 2 prevents this vortex. A flow profilethat is symmetrical with respect to the horizontal center plane of theprocess chamber 1 is created in the region of the inlet zone EZ,homogenized into a parabolic flow profile up to the limit represented bythe dashed line.

The ratios of the sizes of gas inlet zone 6, gas inlet zone 7 and gasinlet zone 8 in relation to one another is preferably 4:15:4.

All disclosed features are (in themselves) pertinent to the invention.The disclosure content of the associated/accompanying priority documents(copy of the prior application) is also hereby incorporated in full inthe disclosure of the application, including for the purpose ofincorporating features of these documents in claims of the presentapplication.

1. A device for depositing crystalline layers on one or more substratesin a process chamber, said process chamber comprising a ceiling and aheated floor that is vertically opposite the ceiling and receives thesubstrates, said device comprising: a gas inlet member disposed atsubstantially the center of the process chamber, which forms gas inletzones disposed vertically one above the other for introducing at least afirst and a second gaseous starting material separately from oneanother; a bottom gas inlet zone neighboring the floor of the processchamber for introducing a first starting material into the processchamber; a top gas inlet zone neighboring the ceiling of the processchamber also for introducing the first starting material into theprocess chamber; a middle gas inlet zone between the top gas inlet zoneand bottom gas inlet zone for introducing the second starting materialinto the process chamber; a single supply of a hydride connected to boththe bottom and the top gas inlet zones, the hydride being the firststarting material; a supply of a metalorganic compound connected to themiddle gas inlet zone, the metalorganic compound being the secondstarting material; at least one substrate carrier arranged around thegas inlet member, being rotationally driven around its axis and carryingthe one or more substrates; and wherein the starting materials flow in ahorizontal direction together with a carrier gas through the processchamber, the stream of gas being homogenized and the starting materialsat least partially pre-decomposed in an inlet zone directly adjacent thegas inlet member, the decomposition products of which starting materialsare deposited on the substrates in a growing zone adjacent the inletzone, while the stream of gas is steadily depleted.
 2. A method fordepositing crystalline layers on one or more substrates in a processchamber, said process chamber comprising a ceiling and a heated floorwhich is vertically opposite the ceiling and on which the substrateslie, said method comprising the steps of: positioning a gas inlet memberat substantially the center of the process chamber for introducing atleast a first and a second gaseous starting material into the processchamber through gas inlet zones disposed vertically one above the otheron the gas inlet member; arranging one or more substrates in arotationally symmetric manner around said gas inlet member; rotatingeach substrate; introducing said first gaseous starting material througha bottom gas inlet zone neighboring the floor of the process chamber anda top gas inlet zone neighboring the ceiling of the process chamber,wherein the first starting material is a hydride, and wherein said firstgaseous starting material is introduced through both the bottom gasinlet zone and the top gas inlet zone from a single supply; introducingsaid second gaseous starting material through a middle gas inlet zonebetween the bottom gas inlet zone and the top gas inlet zone, whereinthe second starting material is a metalorganic compound; and wherein thestarting materials flow in a horizontal direction together with acarrier gas through the process chamber, the stream of gas beinghomogenized and the starting materials at least partially pre-decomposedin an inlet zone directly adjacent the gas inlet member, thedecomposition products of which starting materials are deposited on thesubstrates in a growing zone adjacent the inlet zone, while the streamof gas is steadily depleted; and wherein the steps of introducing thestarting materials are performed in order to reduce the horizontalextent of the inlet zone.
 3. The device according to claim 1,characterized in that the first starting material is AsH₃, PH₃ or anNH₃.
 4. The device according to claim 1, characterized in that thedecomposition product of the first starting material is an element ofthe group V or VI and the decomposition product of the second startingmaterial is an element of the group III or II.
 5. The device accordingto claim 1, characterized in that at least one of the first and thesecond starting material is respectively introduced into the processchamber by means of a carrier gas through the gas inlet zone associatedwith it.
 6. The device according to claim 1, characterized in that thefirst starting material is introduced into the process chamber in aconcentration that is 100 to 5000 or 1000 to 5000 times higher than thesecond starting material.
 7. The device according to claim 1,characterized in that the vertical size of the bottom gas inlet zone orthe top gas inlet zone is less than the vertical size of the middle gasinlet zone.
 8. The device according to claim 7, characterized in thatthe sum of the two sizes of the bottom and top gas inlet zones is lessthan the size of the middle gas inlet zone.
 9. The device according toclaim 1, characterized in that the floor of the process chamber forminga substrate holder is heated from below.
 10. The device according toclaim 1, characterized in that the process chamber has an axialsymmetry.
 11. The device according to claim 10, characterized in thatthe substrate holder is rotationally driven about the center of theprocess chamber.
 12. The device according to claim 10, wherein amultiplicity of circular disk-shaped substrate carriers are disposednext to one another in the circumferential direction on the substrateholder and carry one or more substrates.
 13. The device according toclaim 12, characterized in that each substrate carrier carries sevencircular substrates and altogether six or more substrate carriers areassociated with the substrate holder, located close to one another inuniform circumferential distribution.
 14. The device according to claim1, characterized in that the zone of the maximum growth rate liesradially within the annular growing zone in the marginal region of theinlet zones.
 15. The device according to claim 14, characterized in thatthe diameter of the inlet zone is less than the radial extent of thegrowing zone.
 16. The method according to claim 2, characterized in thatthe first starting material is one of AsH₃, PH₃ and NH₃.
 17. The methodaccording to claim 2, wherein at least one of the first and the secondstarting material is respectively introduced into the process chamber bymeans of a carrier gas through the gas inlet zone associated with it.18. The method according to claim 2, wherein the vertical size of thebottom gas inlet zone or the top gas inlet zone is less than thevertical size of the middle gas inlet zone.
 19. The method according toclaim 2, wherein the floor of the process chamber forming a substrateholder is heated from below.
 20. The method according to claim 2,characterized in that the process chamber has an axial symmetry.